Is (hazardous) terrain damage preventable? - By cowering? (I imagine so, rulebook seems to allow it) - By an Order Card ? (immediate like Intercept ('prevent 20 dmg')) if not your turn, standard (like Battle Ready, attach then remove) or minor (Into the Fray) if during your turn and the creature's activation?)

Specifically in the answer I'm trying to understand if terrain damage is a stack thing; that's how I would justify being ableto use an order card. Even, if it was my turn and my creature had only moved (yes, say stupidly on purpose right onto a hazard) but then as the stack is "take 10 dmg" I could slap "into the fray" to move its speed thus, after resolving, the hazard wouldn't be under my creature anymore?

I have this same question about creature powers that trigger, like the Disciple of Kyuss "take 10 dmg if you end your activation next to it" - what if I did want to end my activation there, and my creature was untapped - could I respond to the 10 damage with an immediate to negate?

Those abilities do trigger and go on the stack, but even on your own activation you can only use Immediates as a response - to play a Minor or Standard, the stack has to be empty. (This is not at all clear from the rulebook, sadly, but was clarified here on the boards.) So you can't use something like Into the Fray to avoid damage.

Other than that, anything that goes on the stack can be chosen as a source, and any preventable damage can be cowered, so you can cower or use an immediate to avoid damage from hazardous terrain or the Disciple of Kyuss.

Minors and Standard, "the stack must be empty". Do you have any reference(s) ? That statement should definitely be more widespread, it's a huge rule and simplifies explanations... big time. For Standards its not a huge change, as most everyone knows that for a Standard you need to tap, and thus in almost all cases that means you really only play a Standard "first". But minors...

So I want to also be crystal clear - does that mean a Minor cannot be played during the response phase in a stack, correct? Or restated, I can teach and be taught that "when an action is about to resolve (aka goes onto the stack), you can only play immediates or cower in response, that's all". And this is regardless of whose turn it is, and whose activation it is! If you played a standard, the opponent can only respond w/ immediates or cower for damage prevention. If you are on the receiving end of an attack (say), you similarly can only look for immediates, or cower. Players should *not bother looking at anything other than immediates* in response to things... all that is correct?.. and to close off all loose ends, movement is NOT a valid immediate correct? Even if it is your turn and your creature is activated and it hasn't moved yet?

I also have the same understanding as Ultville, and the way I understand it (maybe I can find the quote with some digging) is that only immediate actions are played at immediate speed, and therefore only they can be used to respond to things. "Things" usually being attacks, but things also could be "taking damage from fire".

And yes cowering is sort of this weird speedless process where instead of taking the damage it's coverted to morale loss, but that's the very last descision of the player taking damage at that time. It is referred to by the rule book as a way to prevent damage, so anytime "damage cannot be prevented" then you cannot choose to cower an attack.

Found it:

The situation that brought this one up: I'm activating my Drider and put Faerie Fire on my opponent's Dwarf Cleric, which resolves. Then I tap the Drider and play Shadowy Ambush, attempting to hit the Dwarf for a lethal 60. My opponent reasonably responds by using the Cleric's ability, targeting Faerie Fire to attempt to reduce the damage by 10. Can I respond with Quick Jab?

You cannot respond with Quick Jab. It is not played at immediate speed. It cannot interrupt things.

Similarly, could I have used Quick Jab first and responded with a standard action attack to a similar attempt? If I attack an opponent and they respond with a potentially lethal Riposte, could I use my move for the turn to move out of melee range, or use Into The Fray to escape?

You can't use standards to interrupt things on the stack. Only immediate cards.

3. When do priority stops actually happen in Dungeon Command? For example, is there an equivalent of the end step priority window in Magic? The rulebook is pretty clear that you can respond to all discrete actions during the activation phase, but what about other phases? It seems like triggers can happen any time (like the Shadow Stalker power on the Shadow Mastiff that's used as the rulebook's example) but can you add immediate abilities to the stack then?

You can play immediate cards at any point. Normally it is in reaction to an action, but at any point you could do it.

Again, the situation that caused the question: My opponent has an injured creature. During her Deploy phase, she places a Dwarf Cleric adjacent to the injured creature. Is there a priority stop in the Deploy phase such that she can activate the Cleric, so that she can untap it in her Cleanup phase?

Yes, the cleric could deploy and immediately tap to heal an adjacent creature, then untap during your cleanup phase.